Over the years, halogenated hydrocarbons, including chlorinated hydrocarbons such as trichloroethylene, have been accumulating in the environment, particularly in groundwaters. As a result, pollution of water by halogenated hydrocarbons has become an important environmental problem. Contaminated groundwaters represent a large portion of environmental remedial action plans throughout the world.
Dehalogenation of halogenated hydrocarbons by elemental iron to generate innocuous products is known. For instance, dechlorination of trichloroethylene by iron produces reaction products such as ethylene, ethane, and chloride ion. The use of iron in the reaction affords little environmental threat. Thus, it is desirable to be able to efficiently dechlorinate groundwater contaminates using iron.
Recently, Gillham and O'Hannesin disclosed in U.S. Pat. No. 5,266,213, a method for cleaning halogenated contaminants from groundwater. The process involves feeding contaminated groundwater through a trench containing a metal such as iron, under strict exclusion of oxygen, and over a lengthy period of time. Disadvantages of this system are that large amounts of iron are needed for completion of the reactions, as well as, substantial periods of reaction time are required.
Commonly owned, copending application, titled "Enhanced Remediation of Aqueous Compositions Contaminated with Halogenated Hydrocarbons," discloses a method which reductively reacts chlorinated hydrocarbons with metallic iron in the presence of citric acid to generate innocuous byproducts. Also disclosed in commonly owned, copending application titled "Dechlorination of Chlorinated Hydrocarbons by Soluble Iron Citrate," is a method utilizing a preformed ferrous citrate complex to generate chloride ion and rapid degradation of chlorinated hydrocarbons.
It has now been discovered that commercially available iron(II) oxide can dehalogenate hydrocarbons, such as trichloroethylene, trichloroethane, cis and 1,1 dichloroethylene, and brominated aliphatics, in solution at a rapid rate. The rate can be further accelerated by adding at least about 0.5 to 1 percent citric acid based on the weight of iron(II) oxide used.